There has been developed various methods for mounting many microelectronic components on a mounting substrate, and one of them is a transfer method (see Japanese Patent Application Laid-Open No. 2002-182580, for example). In the transfer method, many unseparated microelectronic components 220 (including light emitting diodes (LED) 232 and drive circuits 231) are arranged on a transfer substrate 240 as illustrated in a schematic partial cross-section view in FIG. 17, for example. A connection part 239 of the electronic component 220 is provided with a solder ball or solder bump 250. A planarizing film 226 covering the light emitting diodes 232 and the drive circuits 231 is adhered to the transfer substrate 240 by an adhesive layer 241. Reference numeral 221 indicates a relay substrate on which various circuits or wirings 235, 238 are formed. The electronic component 220 in the state is then separated into the state as illustrated in FIG. 18. A resist layer having an opening at which a separation groove 242 is to be formed is formed on the relay substrate 221 in order to separate the electronic component 220. The separation groove 242 is then formed by etching the relay substrate 221 and the electronic component 220 in a dry etching method using the resist layer as etching mask, thereby separating the electronic component 220.
The separated electronic components 220 are then placed on flux above electronic component attachment parts of the flux-applied mounting substrate, and then the solder balls or solder bumps 250 are melted thereby to solder the electronic components 220 to the electronic component attachment parts provided on the mounting substrate.